A Critical Evaluation of the Nitrogen Assimilation Tests Commonly Used in the Classification of Yeasts

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Abstract
The ability of yeasts to assimilate (NH4)2SO4, urea, asparagine, or peptone. from a synthetic medium has been widely used as diagnostic tests in classification. In the past, the medium contained only potassium dihydrogen phosphate, MgSO4, glucose, and one of the N sources. By addition to this medium of 8 pure B vitamins, trace elements, NaCl and CaCl2, all spp. that were studied which previously had been designated by various authors as not able to assimilate (NH4)2SO4, urea, and asparagine were found to do so. When the vitamins were omitted, only one of these species was found capable of continued growth, thus demonstrating that it was the lack of vitamins in the previously used medium which prevented growth from occurring with some spp., and not an inability to use the particular N source in the medium.

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